2.1 Quercus section
Quercus section is the only section includes species in both Old World and New World in this study (Manos et al., 2001). Eleven species in Quercus section were applied LM and SEM measurements in this study (Table 2). Variation of sizes, shapes, and surface ornamentation of pollen in Quercus section is the highest and average pollen size (Lengths of equatorial axis average 28.22 μm and of polar axis average 31.92 μm) is the largest in three sections (Table 3 and 4; Figure 2-6). Pollen shapes tend to be spheroidal. Surface ornamentations of Quercus pollen include psilate-scabrate, scabrate, and scabrate-verrucate. The distribution patterns of elements are both dense and sparse.